Apparatus for making a data-carrying optical disk

ABSTRACT

An optical disk having a pair of axially oppositely directed faces and an annular outer periphery is made by first forming a mold cavity corresponding to the shape of the disk between a pair of axially spaced parts and a demolding ring sandwiched between the parts. The cavity is then filled with a hardenable resin such that the parts form the respective faces and an inner periphery of the ring forms the outer periphery of the disk and the resin is at least partially hardened in the cavity. The parts are then axially oppositely separated from each other and from the disk to leave the disk in the ring with both of its faces exposed and the ring is then transversely displaced with the disk engaged in it out from between the mold parts. The disk is then cooled and shrunk such that its outer periphery separates from the inner periphery of the ring and the disk separates from the ring.

FIELD OF THE INVENTION

The present invention relates to the manufacture of a data-carryingoptical disk. More particularly this invention concerns a system fortaking the finished disk out of the mold it is formed and/or finishedin.

BACKGROUND OF THE INVENTION

A standard optical disk is made between a pair of mold parts, one ofwhich has a surface that embosses in the resin the disk is made frombumps that carry the disk's data. The hot resin may be cured withultraviolet light. Once the disk is formed, the mold is opened,invariably leaving the disk stuck to the mold part having thedata-forming bumps.

Stripping the disk from the mold is a fairly delicate task because thestill-hot disk is extremely fragile, and also because the data-carryingformations are very minute. At the same time the disk must be handledwith reasonable speed to free the mold to make another disk, as themolds are so very expensive that they cannot be left idle. Using asuction-type lifter or gripper is one proposed method that frequentlyspoils the somewhat soft disk.

German patent document 2,917,042 filed 27 Apr. 1979 by GuntherSchauffeld (citing U.S. Pat. Nos. 4,124,352 and 3,830,613) describes asystem where a punch physically knocks a molded workpiece out of a mold.Such an arrangement is fairly crude and, indeed, this patent documentdoes not deal with a delicate optical disk but with a more ruggedworkpiece.

In German patent document 3,027,568 filed by Egbert Broeksoma et al witha claim to a Dutch priority date of 10 Aug. 1979 an arrangement isdescribed whereby grippers engage the edges of an optical disk and peelit off one of the mold parts after it has cured somewhat. Thisarrangement deforms the disk considerably and can, therefore, damage it.

PCT publication WO 88/01564 (citing U.S. Pat. Nos. 4,519,767, 4,283,973,and 4,441,949) also grips the edges of the disks as they are beingprocessed, but does not describe how the disks are stripped from themold they are originally produced in.

Finally, European patent application publication 339,616 injects airbetween the disk and the mold part it is stuck to to free it therefrom.This procedure is relatively gentle, but still does substantially deformthe disk so that it can be damaged, especially as it is still fairly hotand plastically deformable when it is being separated from the mold.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved method of and system for molding an optical disk.

Another object is the provision of such an improved method of and systemfor molding an optical disk which overcomes the above-givendisadvantages, that is which allows the disk to be stripped from itsmold without substantially deforming it or touching either of its faces.

SUMMARY OF THE INVENTION

A method of making an optical disk having a pair of axially oppositelydirected faces and an annular outer periphery according to the inventioncomprises the step of first forming a mold cavity corresponding to theshape of the disk between a pair of axially spaced parts and a demoldingring sandwiched between the parts. The cavity is then filled with ahardenable resin such that the parts form the respective faces and aninner periphery of the ring forms the outer periphery of the disk andthe resin is at least partially hardened in the cavity. The parts arethen axially oppositely separated from each other and from the disk toleave the disk in the ring with both of its faces exposed and the ringis then transversely displaced with the disk engaged in it out frombetween the mold parts. The disk is then cooled and shrunk such that itsouter periphery separates from the inner periphery of the ring and thedisk separates from the ring.

With this system therefore there is no need to make any physical contactwhatsoever with either of the faces of the disk. The ring gripping theedge holds it solidly enough to allow the two mold parts to peel awayfrom the disk faces, and once the disk cools and shrinks slightly, itseparates sufficiently from the ring to drop out, without being touchedon its delicate faces.

According to another feature of this invention during and after thecuring and cooling step another such ring is aligned between the partsand same are closed on it to form the cavity. Then the remaining stepsof the method are sequentially repeated with the other such ring to makeanother disk, all while the first one is cooling. Clearly there can be aplurality of such second rings to allow plenty of time for thecooling/shrinking step. The rings outside the mold can be axiallyaligned with one another or can all lie in the same plane, being carriedon a common drum-like support.

The apparatus according to this invention therefore has a pair ofaxially spaced and axially relatively displaceable mold parts and a ringaxially alignable between the parts and having an inner peripheryforming with the parts a substantially closed mold cavity correspondingto the shape of the disk. Means is provided for axially oppositelyseparating the parts from each other and from the disk to leave the diskin the ring with both of its faces exposed after at least partialhardening of the resin in the cavity and for transversely displacing thering with the disk engaged in it out from between the mold parts.

Furthermore according to this invention the inner periphery of the ringcan be radially inwardly concave or convex. The ring can also beprovided with at least one latching element radially displaceablebetween an inner position projecting radially inward past the innerperiphery and an outer position not projecting radially inward past theinner periphery.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following, it being understood that anyfeature described with reference to one embodiment of the invention canbe used where possible with any other embodiment and that referencenumerals or letters not specifically mentioned with reference to onefigure but identical to those of another refer to structure that isfunctionally if not structurally identical. In the accompanying drawing:

FIG. 1 is a partly sectional side view of the system of this invention;

FIG. 2 is a large-scale view of the detail indicated at II in FIG. 1;

FIGS. 3 and 4 are views like FIG. 2 of variants on the apparatus of thisinvention; and

FIG. 5 is a small-scale diagrammatic view of an alternative arrangementaccording to the invention.

SPECIFIC DESCRIPTION

As seen in FIGS. 1 and 2 a pair of mold parts 1 and 2 aligned along anaxis A can be moved toward and away from each other axially byrespective actuators shown schematically at 9 and 10. An extruder shownschematically at 11 can feed a liquefied synthetic resin to the part 1.

According to the invention a mold ring 4 is held on a support 5 betweenthe two mold parts 1. The two parts 1 and 2 can be closed axially on thering 4 to form therewith a mold cavity having one axial side delimitedby the part 1, an opposite axial side delimited by the part 2, and anouter periphery delimited by an inwardly concave periphery 6 of the ring4. The extruder 11 can fill this cavity with the resin to form aworkpiece disk 3, here an optical disk carrying information in the formof surface irregularities imparted by the face of the part 1 and/or 2.

Once the disk 3 thus formed has hardened sufficiently to maintain itsshape at ambient temperature, the two parts 1 and 2 are axiallyseparated from each other, leaving the disk 3 in the ring 4 with bothfaces of the disk 3 separated from the respective mold parts 1 and 2.Then the support 5 swings the ring 4 out about an axis A' parallel tothe axis A and simultaneously swings another such ring 4' into positionbetween the parts 1 and 2. The parts 1 and 2 can then be closed on thenew ring 4' while the disk 3 in the ring 4 cools and another disk can bemolded.

The depth of the inwardly open groove forming the inner periphery 6 isvery slight so that, as the disk 3 cools and shrinks, it pulls away fromthis periphery 6, freeing the disk 3 from the ring 4. The cured and cooldisk will drop easily from the ring 4 so that the process can berepeated.

It is of course possible to provide more than two such rings 4, 4' whichare axially aligned with one another when not in the mold. Alternatelyas shown in FIG. 5 a holder 5' can carry a plurality of rings 4"identical to the ring 4 which are stepped angularly about the axis A',so that at any time one ring 4" is in the mold and the remaining onesare outside it but in the same plane perpendicular to the axes A and A'.

Furthermore as seen in FIG. 3 a ring 4a can be used having an innerperiphery 7 that is radially inwardly convex, not concave. Thisformation will produce a disk whose outer edge is outwardly concave,opposite to the shape of the disk 3 produced by the ring 4.

FIG. 4 shows ring 4b with a radially inwardly projecting latch pin orelement 8 that can be moved radially outward as indicated by the arrowto free a disk held in the ring 4b. This system is useful if theshrinkage of the resin is small and extra hold is necessary.

We claim:
 1. An apparatus for making an optical disk having a pair ofaxially oppositely directed faces and an annular outer periphery, theapparatus comprising:a pair of axially spaced and axially relativelydisplaceable mold parts; a ring axially alignable between the parts andhaving an inner periphery forming with the parts a substantially closedmold cavity corresponding to the shape of the disk; means for fillingthe cavity with a hot hardenable resin that shrinks when cooled, wherebythe parts form the respective disk faces and an inner periphery of thering forms the outer periphery of the disk, one of the peripheries beingradially concave and the other of the peripheries being complementaryradially convex, whereby the disk outer periphery is captured in thering inner periphery; means for axially oppositely separating the partsfrom each other and from the disk to leave the disk in the ring withboth of the disk faces exposed after at least partial hardening of theresin in the cavity; and means for transversely displacing the ring withthe disk engaged in the ring out from between the mold parts, the innerperiphery of the disk having a diameter such that on cooling andshrinking the outer periphery of the disk separates from the innerperiphery of the ring and the disk separates from the ring.
 2. Thedisk-making apparatus defined in claim 1 wherein the inner periphery ofthe ring is radially inwardly concave.
 3. The disk-making apparatusdefined in claim 1 wherein the inner periphery of the ring is radiallyinwardly convex.
 4. The disk-making apparatus defined in claim 1 whereinthe ring is provided with at least one latching element radiallydisplaceable between an inner position projecting radially inward pastthe inner periphery and an outer position not projecting radially inwardpast the inner periphery.
 5. The disk-making apparatus defined in claim1, further comprising:an additional ring, and means for transverselydisplacing the additional ring into axial alignment with the mold parts.6. The disk-making apparatus defined in claim 1 wherein there are aplurality of rings, the apparatus further comprisingmeans for displacingthe rings between an inner position axially aligned with the mold partsand an outer position axially out of alignment with the mold parts. 7.The disk-making apparatus defined in claim 6 wherein in the outerposition the rings not aligned between the mold parts are aligned withone another.
 8. The disk-making apparatus defined in claim 6 wherein therings all lie in a common plane and are displaced jointly.